Alaa:
Anything you add to users using wix-users.register will create a record in the dashboard CRM. The problem is that you are creating a copy on your web site so if you change information you keep on your web site in the CRM on your dashboard then you will create synchronisation problems. If you are simply using the CRM for sending triggered Emails and shoutOuts then you should be OK. The CRM APIs as they currently exist are write only from your page.
Cheers
Steve